The PbSb2Se4–Pb5Bi6Se14 section of the Sb2Se3–PbSe–Bi2Se3 quasi-ternary system

Abstract

The PbSb₂Se₄–Pb₅Bi₆Se₁₄ section of the Sb₂Se₃–PbSe–Bi₂Se₃ quasi-ternary system was studied by integrated physicochemical analysis methods, and the state diagram of this section was constructed. The PbSb₂Se₄–Pb₅Bi₆Se₁₄ section was found to be a partially quasi-binary section of the Sb₂Se₃–PbSe–Bi₂Se₃ quasi-ternary system. A region of solid solutions based on PbSb₂Se₄ at room temperature was detected at 10 mol % Pb₅Bi₆Se₁₄. At a ratio between the initial components of 1: 1, congruently melting quaternary compound Pb₆Sb₂Bi₆Se₁₈ forms. Its single crystals were produced by the method of chemical transport reactions. Pb₆Sb₂Bi₆Se₁₈ crystallizes in the rhombic system with the unit cell parameters a = 14.43 Å, b = 21.42 Å, c = 3.90 Å, V⁰ = 1205 ų, Z = 4, and space group Pnnm. The thermodynamic functions of Pb₆Sb₂Bi₆Se₁₈ were calculated: the standard entropy S₂₉₈⁰ = 1472.8 J mol^–1 K^–1, the enthalpy ΔH₂₉₈⁰ =–1215.8 kJ mol^–1, and the Gibbs free energy of formation ΔG₂₉₈⁰ =–1193.6 kJ mol^–1.